The invention relates to a control valve for a fuel injection nozzle, having a control chamber with a valve seat, into which a fluid conduit discharges. A valve element, which rests on the valve seat in the control chamber, so that the fluid conduit is closed. An armature plate, which is disposed in a damping chamber and has a pressure piece that cooperates with the valve element, and having an armature coil.
A control valve of this kind is used in a fuel injection nozzle, for example for a common rail system for diesel engines, to control the opening and closing of the nozzle needle of the injection nozzle. The fluid conduit discharges into the control chamber and leads to a pressure chamber, which is closed on one side by the nozzle needle or by a component connected to the nozzle needle. When the valve element of the control valve is closed, no fluid can escape from the pressure chamber via the fluid conduit, so that the fluid is backed up in the pressure chamber. As a result, an adequately high pressure in the pressure chamber keeps the nozzle needle in the closed position. Conversely, when the valve element lifts from the valve seat, the backed-up fluid escapes from the pressure chamber through the fluid conduit and the control chamber of the control valve, the pressure in the pressure chamber drops, and as a result, the nozzle needle, under the influence of the fuel pressure applied to an upstream end of the nozzle needle, is lifted from its nozzle needle valve seat. Fuel can now be injected into a cylinder of an engine.
To enable controlling the injection event with the requisite speed, fast switching of the control valve is desirable. The chronological spacing between two injection events, for instance between a preinjection and the subsequent main injection, is defined by the length of time that the armature of the control valve, comprising the armature plate and the pressure piece, requires to return to a standstill after a closing motion, or in other words after the closing motion has pressed the valve element against the valve seat. Since in fact the armature, toward the end of the closing motion, abruptly strikes the valve element or a similar stop, the result can be a bouncing of the armature, which is disadvantageous for the next triggering of the control valve. To prevent the bouncing and to reduce the length of time that the armature needs to return to a standstill, it is for instance known from the prior art to embody the pressure piece and the armature plate separately, and to use a spring to decouple the pressure piece from the armature plate in a suitable way. However, the armature plate, which can vibrate in the closing motion and does not come to a standstill until after a certain calming time, still remains.
An object of the invention is to further develop a control valve of the type defined at the outset such that shorter switching times are possible.
A control valve according to the invention leads to a controlled braking of the closing motion of the armature, thus overcoming the risk of bouncing. It is thus no longer necessary to embody the pressure piece and the armature plate separately from one another, and the result is accordingly a simplified and hence more economical construction. The functional reliability is also enhanced, since the armature and plate, now in the form of a one-piece component, is more stable.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawing.